The invention relates to a medical instrument comprising a tubular body housing at least one injection needle.
A medical instrument of this type in the form of a catheter is known from U.S. Pat. No. 5,538,504.
This catheter has a tubular body housing one injection needle with a radially outwardly directed tip portion in an axially undisplaceable manner, and has a control element for deploying the tip of the injection needle out sideways from the tubular body.
A tubular body of the catheter houses inside it an injection needle which has a radially outwardly directed tip portion. In the tubular body there is a corresponding opening, via which at least the tip of the outwardly directed tip portion can pass through radially outwards. Provided in the region of the outwardly directed tip portion is a control element, by means of which the tip portion can be pressed radially outwards as and when required.
Without actuation of the control element, the outwardly directed tip portion is fully retracted in the tubular body. In this state, the catheter can be pushed into a vessel, for example into a urethra.
The control element comprises an inflatable balloon, which is situated in the catheter directly alongside the outwardly directed tip portion. If the balloon is inflated, whether by means of a liquid or a pressurized gas, the inflated balloon presses the tip portion radially outwards, so that at least the tip moves radially outwards beyond the outer side of the tubular body and punctures the vessel. A medicament can then be administered.
After application, the liquid or the pressurized gas is let out again, so that the balloon can contract. The return of the outwardly directed tip portion then takes place on the basis of the elasticity of the outwardly directed tip portion, which usually consists of metallic material.
A disadvantage of this is that it cannot be ensured with absolute certainty that the outwardly directed tip portion will move back again completely into the tubular body.
This is because the tip has punctured the tissue of the vessel and is held relatively firmly there.
This can have fatal consequences when the medical instrument is withdrawn from the vessel, to be specific that the vessel may be damaged, or even lacerated, by the tip still protruding beyond the outer side of the tubular body over the entire length over which it is withdrawn.
From WO 92/10142 it is known to move a number of injection needles out of a tubular body in a circumferentially distributed manner, so that in the case of a relatively large vessel it can be supplied with a medicament at multiple locations circumferentially. Here, the retraction and deployment is controlled by an axial longitudinal displacement of the injection needles. Provided for this purpose in the tubular body is a control element with recessed channels, in which the injection needles can be moved axially back and forth. In the region of the lateral outlets, these channels have outwardly directed curvatures, over which the injection needles then emerge from the tubular body in an outwardly directed manner.
A disadvantage of this structural design is that the injection needles must be axially displaced back and forth in the tubular body, which is problematic in the case of extremely thin injection needles and can lead to them becoming caught or stuck. Considerable design measures have to be taken here to make sure that, before the medical instrument is withdrawn, it is ensured that all the injection needles are fully retracted again.
In the case of the subject matter of the present application, the intended area of use is as an anuscope, i.e. the tubular body is of a considerable length and a considerable diameter and serves the purpose of applying a medicament in a circumferentially distributed manner in the rectum.
If tips of the injection needles were still to protrude radially beyond the tubular body when the instrument is withdrawn from the anus, considerable injuries would occur.
It is therefore an object of the present invention to develop a medical instrument of the above-mentioned type in that the outwardly directed tip portions of the injection needles are moved in a defined manner into the deployed position, and back into the fully retracted position.